1. Field of the Invention
The present invention relates to a gate driver for driving the gate of a switching element and to a semiconductor device employing the gate driver.
2. Description of Related Art
Recent output transistors used in, for example, switching power sources carry out high-speed switching to cause a large counter electromotive voltage that produces a surge voltage between the drain and source of the output transistor when the transistor is turned off to open the drain and source thereof. Such a surge voltage may break the transistor, and therefore, the transistor must have a means to protect the transistor from the surge voltage.
In connection with this, Japanese Unexamined Patent Application Publication No. H08-288817 (Patent Document 1) discloses a semiconductor device for disconnecting an inductive load at high speed from a high-side switch and a technique of suppressing a drain-source voltage of the high-side switch. In “Description of Related Art” of Patent Document 1, there is mentioned an active clamp circuit of a constant voltage element and a diode that are connected in series. The active clamp circuit is arranged between the drain and gate of a high-side switch, to suppress a drain-source voltage of the high-side switch and protect the high-side switch from a surge voltage.
Japanese Unexamined Patent Application Publication No. 2001-245466 (Patent Document 2) mentions about a power conversion apparatus that suppresses and lowers an excessively high surge voltage generated when an IGBT or a MOSFET is switched at high speed. This power conversion apparatus adopts an active clamp circuit applicable to either of high-side and low-side switches. The active clamp circuit connects a capacitor in parallel with a diode, to speedily form a negative feedback path and clamp an overvoltage.